Present day motion detector devices rely upon the Doppler principle, as is well known within the art, to detect the presence of a moving object within a protected volume or volume to be surveyed. Conventionally, such motion detector devices use at least microwave technology, that is, typically X-band or K-Band signals transmitted and received via a transceiver. Post-reception, the received signals are suitably processed to identify the presence of a Doppler signal that can be attributed to movement within the protected volume.
Relatively sensitive devices such as, for example, the mixer, which typically takes the form of a mixer diode, can be easily damaged by inappropriate handling or excessive signal strengths. Therefore, care needs to be taken in the fabrication and the installation of the motion detector devices. Notwithstanding any such care, the mixer diodes may, post-installation, be inappropriately exposed to signals or handling that may cause damage. It will be appreciated that any such damage may, in the worst case, prevent the motion detector device from operating correctly in that, from the perspective of the output of the mixer diode, there will be no change in the signal due to any Doppler shifted received signal. Alternatively, the performance of the mixer diode may be degraded in some way so that it produces excessive noise which reduces the sensitivity of the motion detector device.
It is an object of the present invention at least to mitigate some of the problems of the prior art.